Download CHEM1101 2010-J-5 June 2010 • Describe the nature of an ionic

CHEM1101
2010-J-5
June 2010
• Describe the nature of an ionic bond in terms of atomic and molecular orbitals.
When a covalent bond is formed between two elements of identical
electronegativity, bonding and antibonding orbitals are formed which have equal
contributions from both atoms. The covalent bonding arises from the increase in
electron density between the two atoms.
As the electronegativity difference increases, the bonding orbital has a greater
contribution from the more electronegative element. As a result the electron
density is larger at the more electronegative element and the electron density
between the two atoms is decreased. This decreases the covalent contribution to
the bond.
However, the uneven sharing of the electron density leads to a build up of
negative charge on the more electronegative atom and a build up of positive
charge on the less electronegative atom. As a result, there is an electrostatic
attraction between the atoms: an ionic contribution to the bond.
In the hypothetical case where the electronegativity difference is infinite, the
‘bonding’ orbital becomes the atomic orbital of the more electronegative atom.
The electrons in the orbital are both located on this atom, giving it a full anionic
charge. The other atom then has a full cationic charge. A fully ionic bond results.
2